The present invention relates to membrane switches and in particular to a membrane switch providing for backlit, illuminated buttons.
Membrane switches provide electrical contacts closing when a front flexible membrane is compressed by a finger touch or the like against a rear surface, typically a second membrane. Each of the membranes has electrical contacts printed on their opposing faces at button locations that are brought into electrical conduction when the membrane is flexed, and held apart by the natural elasticity of the membrane and a spacer layer when the front membrane is released.
In some applications, it may be desirable to illuminate the membrane switch, for example, by backlighting the individual buttons. While the membranes themselves may be transparent, the metallic conductors used to create the contacts block light producing shadows on the button face.
The prior art has addressed the problem of shadowing in a number of ways. Most simply the conductive areas of the contacts are moved from alignment with the light conducting areas of the button. In this approach, the light conductive areas must be minimized so as to not unduly limit the available conducting surface of the contacts, and the graphics layer (which defines the light conducting areas of the button) and membrane switch must be designed in tandem, making the design process more expensive and cumbersome.
An alternative approach to eliminating the shadows caused by the membrane switch conductors employs a diffuser or light pipe interposed between the membrane switch and the front graphic layer. While this approach allows for some standardization of the membrane switch components, it increases the complexity of the membrane switch and may undesirably increase the thickness of the switch and change its mechanical properties.
A third approach to providing illuminated membrane switches fabricates an electroluminescent (EL) panel on top of the membrane switch to completely avoid the opaque conductors. This approach requires a relatively complex fabrication process and the use of an electroluminescent panel for the light source.